HCAW aren't the weapon of choice for crazy killers. We have exactly one instance where they were(unless you want to argue Aurora, at which point I'd say "He fired about 30 rounds with his HCAW and wounded/killed 70. That's not a majority" and move on). While it's certainly reasonable that one COULD kill more people with a HCAW than a handgun or a shotgun, that's not what they're using. It's reasonable that a car packed with explosives and detonated in a crowd COULD kill more people than a HCAW but, again, that's not what's being used.

So, to save swamp from himself, there's no evidence that a HCAW ban would reduce mass shootings.

The vast majority of gun crime in America will not be stopped by gun registration. It will have zero impact.

If you want to round up all your citizens guns you need them all registered.

That's not really the point of registering guns. The point is the 2nd part. Huge prison sentences for possessing an unregistered gun. You know criminals aren't registering their gun. And, far too often, they plea down their sentences because the prosecuting attorney feels their case might not be that strong. There's no blurred line with possession of an unregistered gun. You either have it registered or you don't.